Water scarcity is a major constraint to human and agricultural development. Roughly 70% of the fresh water consumed is directed towards agricultural-related usage, for example as irrigation water, which in turn accounts for roughly 90% of agricultural usage. As the demand for fresh water through agricultural development as well as human development increases, more effective uses of water are becoming necessary. This need is even more pronounced in light of the increasing scarcity of fresh water. There is also an increasing demand for fresh water in food production and non-food related raw materials such as biofuel, biomass and renewable biomaterials apart from the aforementioned use. Accordingly, there is a growing need for an improved and more efficient usage of fresh water.
Fresh water is lost in agriculture applications through two main pathways: (1) run-off or evaporation and (2) drainage out of plant root zone. With respect to run-off, the slow or arrested penetration of water into soil will lead to run-off of water where the soil area is, in particular, sloped or angled. Another effect is an accumulation of water on a flat/level soil surface, which allows for water evaporation through extended exposure to the atmosphere. The slow permeation is caused by several mechanisms, such as the destruction of a soil's porous structure, as indicated by soil crust formation. Water repellent soil can develop when the soil becomes hydrophobic and substantially or totally resists the infiltration of water into it.
With respect to drainage, the drainage of water out of the root zone may be caused by a low water holding capacity of the soil and/or uneven distribution of water. The soil water holding capacity is determined by the soil texture and amount of organic matter in soil. For example, usually coarse-textured soils, e.g., sandy soils, have a much smaller water holding capacity than fine-textured soils, e.g., loamy soil. The uneven distribution of water can be caused by the application method of irrigation water (e.g. furrow irrigation) and the heterogeneity of soil composition. Preferential flow may also occur in heterogeneous soils, and it funnels the water supply quickly out of the root zone and causes the inefficiency of water usage.
Several approaches were used in an attempt to increase the agriculture water usage in agriculture, one of which was the use of surfactants. It is generally known that surfactants can reduce the surface tension of the irrigation water, but also face drawbacks, for example as disclosed in (among others) U.S. Pat. No. 5,927,003 to Miller et al., incorporated herein by reference.
It is also known that water-absorbent polymers can assist in improving water management. These absorbent polymers otherwise known as superabsorbents are used to increase water usage efficiency. Superabsorbents have cross-linked polymer network structures, which can hold water several to a few hundred times the original superabsorbent volume. Superabsorbents include hydrolysis products of starch-acrylonitrile graft polymers, carboxymethylcellulose, cross-linked polyacrylates, cross-linked polyacrylamides, polyvinyl alcohols, polyacrylonitrile and polyethylene oxide. Several U.S. patents as described below, for example, disclose a variety of polymers used in agriculture for improving water management.
U.S. Pat. No. 4,985,062 to Hughes discloses an aqueous gel of a cross-linked mixed salt of homopolymerized or copolymerized acrylic acid. U.S. Pat. No. 4,559,074 to Clark discloses a substantially non-ionic polyacrylamide cross-linked with a small amount of methylenebisacrylamide (MBE) or other agent. U.S. Pat. No. 4,124,748 to Fujimoto et al. discloses a cross-linked copolymer of a vinyl ester and an unsaturated carboxylic acid ester, neutralized with a potassium or ammonium alkali, for seed culturing media in plants. U.S. Pat. No. 4,320,040 to Fujita et al. discloses a method of preparing hydro-gel polymers from polyvinyl alcohol and polyacrylic acid to be used as a water-retaining agent for plants or soils.
Superabsorbents are applied as soil additives and are typically buried, manually or mechanically, within the vicinity of root zone. As such, these superabsorbents can swell and hold water when irrigation water is applied, and release the water during the irrigation interval or a dry period. Burying of superabsorbents can typically be accomplished by temporarily removing any plants from the soil, typically done through a gardening-type application. However, the drawbacks with large scale undertakings such as widespread turf and in-ground crop applications are obvious, as it is generally impractical or financially infeasible to remove all or most plants and/or top layer of soil. Further, there is a relatively high cost associated with such applications as large amounts of superabsorbents are generally needed to achieve sufficient performance.
Some have tried to address these drawbacks by implementing devices for injecting superabsorbents in situ. For example, some have used modified or standard tilling machines, water-jet injectors, seed drills and coring machines in an attempt to inject polymers into the soil. However, such methods have proved problematic. The previously described methods can disturb topsoil and shock and destroy plants or turf. As such, these methods are largely unsuitable and require superabsorbent insertion before the turf and/or plants have been laid, planted or grown. In addition, these previously described methods often do not distribute the polymers evenly or efficiently, or in the areas that need superabsorbents the most. This is compounded by the fact that historically, suitable polymers can be relatively expensive and previously described applications cannot apply them in a cost-effective manner.
Accordingly, there is a need for an improved soil additive comprising a polymer network that can target the most advantageous or needed locations in soil (thus increasing effectiveness relative to the amount of polymer utilized) and that can provide improved water usage by plants and grasses.
There is also a need for an improved method or mechanism to apply a polymer within soil that has increased efficacy (relative to the total amount of polymer used), can target the most advantageous or needed locations in the soil and can improved water usage efficiency by plants and grasses.